WA 3 Biology - La Rosa1 Melissa La Rosa Dr Martinez Intro...

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La Rosa1 Melissa La Rosa Dr. Martinez Intro to Biology 2/7/12 Writing Assignment # 3 1. Why is photosynthesis described in terms of light-dependent and light-independent reactions? How do these reactions differ? The light-dependent reaction can only occur in the light because light supplies the energy needed for the reaction. In this stage of photosynthesis, light energy is converted into chemical energy (ATP) and 'reducing power' (NADPH) which are then used in the light-independent reaction. Also in the light- dependent reaction, water is split to provide the hydrogen needed to make NADPH. The light-independent reaction can take place in the light and the dark, i.e., it is independent of the light! However, it needs the products of the light-dependent reaction (ATP and NADPH), so it cannot continue indefinitely without it. In the light-independent reaction, the ATP and NADPH produced by the light- dependent reaction are used to convert carbon dioxide into carbohydrate, e.g., glucose. This happens in a series or reactions called the Calvin cycle. 2. How do the structure and composition of a plant leaf facilitate photosynthesis? Plants are the only photosynthetic organisms to have leaves (and not all plants have leaves). A leaf may be viewed as a solar collector crammed full of photosynthetic cells .Water enters the root and is transported
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